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BMW TECHNOLOGY / Air Damping System
With the new rear strut for the HP2 Enduro,
BMW yet again presents a world
innovation in motorcycle chassis construction.
With the new air damping system,
air exclusively undertakes both
suspension and damping functions -
such a gas spring damper system provides
a weight advantage of nearly 2 kg
compared to conventional struts with
steel helical spring and oil damping: the
innovative component weighs only 2.3
kg in total.
The basic layout of the air damping system
features analogies to conventional
struts: a piston travels in a cylinder, but
displaces instead of oil air that flows
from one chamber into the other. Damping
is achieved when plate valves throttle
this air flow; suspension is obtained
when the trapped air is compressed.
Air as a medium provides the optimal
conditions for use in a spring damper
system.
• Under high load (when the suspension
is highly deflected) and at high
temperatures (over longer use) the
pressure in the system rises, causing
a natural progression of the spring
rate: the higher the pressure in the
chamber, the greater the force
needed for further compression. This
physical behavior therefore ensures
good overload protection that improves
under higher loads.
• Also the increasing viscosity of air
causes under high load a natural progression
of damping at rising temperatures,
but without the risk of
overheating as with conventional
struts.��
• Precisely matching the internal flow
system and the gap throttles gives
rise to frequency-independent and
frequency-selective air damping: the
rear wheel ideally follows all unevenness,
also e.g. over very short and
fast excitations (corrugated metal
track). The optimal ground contact in
every situation means in turn the ideal
transfer of forces during acceleration
and greater braking safety.
• The system's smaller unsprung
masses also exert a positive effect on
the strut's response characteristics
and rear wheel traction.
On the outside the air damping system
consists of an aluminum cylinder that
forms the actual strut with two air chambers
and gastight rubber bellows that
completely seals the strut including the
piston rod.
The system is therefore protected
against soiling, facilitating maintenance
and preventing e.g. dust from abrading
the piston's O ring. The strut is filled with
ambient air through a normal Auto valve;
a high pressure hand pump and pressure
gauge are included with the product.
Varying the filling pressure in the strut
means that the motorcycle can be quite
easily tuned to various loading states or
the seat height can be adjusted. A bubble
on the frame indicates the motorcycle's
normal position as an adjustment
aid. In addition, the only other adjustment
facility is a small hand wheel that
varies the damping characteristics between
the two variants Sport and Competition
by opening up a small bypass
between the air chambers.
BMW MOA
The Essential
BMW Motorcycle
Accessory
Over 40,000 Members and still
growing! Tell a friend about the
largest BMW Motorcycle Owners
Organization in the World.
For membership information
contact
BMW MOA
P.O. Box 3982
Ballwin, MO 63022
USA
(636) 394-7277
www.bmwmoa.org
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